Glucocorticoid receptor expression in the postnatal rat cochlea

Genetically Predicted Sleep Traits and Sensorineural Hearing Loss: A Mendelian Randomization Study

OBJECTIVE

Observational studies suggest a potential association between sleep characteristics, sensorineural hearing loss (SNHL), and sudden SNHL (SSNHL), but causal evidence is scarce. We sought to clarify this issue using two-sample Mendelian randomization analysis.

METHODS

The inverse-variance weighted (IVW) method was performed as primary analysis to assess bidirectional causal associations between sleep traits (chronotype, sleep duration, insomnia, daytime sleepiness, and snoring) and SNHL/SSNHL using publicly available Genome-Wide Association Studies summary data from two large consortia (UK Biobank and FinnGen). Sensitivity analyses, including Mendelian randomization (MR)-Egger, Mendelian randomization pleiotropy residual sum and outlier, weight median, Cochran's Q test, leave-one-out analysis, and potential pleiotropy analysis, were conducted to ensure robustness.

RESULTS

IVW analysis found suggestive associations of morning chronotype (odds ratio [OR] = 1.08, 95% confidence interval [CI] = 1.01-1.16, p = 0.031) and daytime sleepiness (OR = 1.88, 95% CI = 1.24-2.87, p = 0.003) with SNHL onset. Additionally, morning chronotype was nominally associated with SSNHL onset using IVW method (OR = 1.37, 95% CI = 1.10-1.71, p = 0.006). However, there was no evidence for the causal effect of SNHL and SSNHL on different sleep traits (all p > 0.05). Sensitivity analysis showed that the results were stable.

CONCLUSION

Within the MR limitations, morning chronotype and daytime sleepiness were underlying causal contributors to the burden of SNHL, indicating that optimal sleep might facilitate the prevention and development of SNHL.

LEVEL OF EVIDENCE

3 Laryngoscope, 2024.

Cochlear implant surgery facilitates intracochlear distribution of perioperative systemic steroids

BACKGROUND

Systemically administered steroids are widely utilised for hearing preservation therapies. More recently, steroids have been administered to achieve hearing protection after cochlear implant surgery. Currently there is a lack of understanding as to which administration route offers most therapeutic efficacy, local or systemic administration. Paramount to this are observations in animal studies that systemic administration following implantation offers hearing protection and reduced cochlear fibrosis, despite observations that perilymphatic levels are up to 10-fold higher after local administration in non-implanted cochleae.

AIMS/OBJECTIVES

This paper explores the impact that cochlear implantation and associated acute inflammation has on steroid distribution and uptake following systemic administration of dexamethasone.

MATERIAL AND METHODS

Eight guinea pigs received systemic dexamethasone 60 min prior to cochlear implantation. Implanted and contralateral non-implanted cochlea were harvested for tissue immunohistochemistry and detection of dexamethasone.

RESULTS

Cochleostomy with scala tympani implantation resulted in a significant increase in cochlear dexamethasone signal. This was most notable at the organ of Corti, stria vascularis, and blood product in the scala tympani.

CONCLUSIONS AND SIGNIFICANCE

This study demonstrates that the inner ear distribution of systemically administered steroids is enhanced following surgery for cochlear implantation and provides rationale for systemic perioperative steroids in hearing preservation surgery.

Immunohistochemical localization of glucocorticoid receptors in the human cochlea

In the present study we investigated the localization of glucocorticoid receptors (GCR) in the human inner ear using immunohistochemistry. Celloidin-embedded cochlear sections of patients with normal hearing (n = 5), patients diagnosed with MD (n = 5), and noise induced hearing loss (n = 5) were immunostained using GCR rabbit affinity-purified polyclonal antibodies and secondary fluorescent or HRP labeled antibodies. Digital fluorescent images were acquired using a light sheet laser confocal microscope. In celloidin-embedded sections GCR-IF was present in the cell nuclei of hair cells and supporting cells of the organ of Corti. GCR-IF was detected in cell nuclei of the Reisner's membrane. GCR-IF was seen in cell nuclei of the stria vascularis and the spiral ligament. GCR-IF was found in the spiral ganglia cell nuclei, however, spiral ganglia neurons showed no GCR-IF. Although GCRs were found in most cell nuclei of the cochlea, the intensity of IF was differential among the different cell types being more intense in supporting cells than in sensory hair cells. The differential expression of GCR receptors found in the human cochlea may help to understand the site of action of glucocorticoids in different ear diseases.

Glucocorticoid receptor (NR3C1) genetic polymorphisms and the outcomes of sudden sensorineural hearing loss

BACKGROUND

The glucocorticoid receptor gene (NR3C1) encodes the receptor to which cortisol and other glucocorticoids bind. Steroids in either oral, intratympanic, or intravascular forms are the treatment of choice for sudden sensorineural hearing loss (SSNHL), but the outcome varies. The outcomes of SSNHL have been investigated for related factors, including age, initial hearing loss severity and pattern, vertigo, genetic variations, and the time between onset and treatment. The objective of the present study was to analyze the association of genetic polymorphisms of NR3C1 with the outcomes of SSNHL.

MATERIALS AND METHODS

We conducted a comparison study of 93 cases with a poor outcome (control) and 100 cases with a good outcome (case) in SSNHL patients. Six single nucleotide polymorphisms (SNPs) were selected. The genotypes were determined using TaqMan technology.

RESULTS

The heterozygous AT genotype of rs17100289 was associated with a poor outcome in comparison with the major homozygous AA genotype after adjustments for age and sex (OR = 0.50; 95% CI 0.26-0.95; P = 0.035) in SSNHL patients. The CT genotype of rs4912912 was also associated with a poor outcome compared with the major homozygous TT genotype after the adjustments (OR = 0.47; 95% CI 0.24-0.92; P = 0.026).

CONCLUSION

These results suggest that NR3C1 genetic polymorphisms may influence the outcomes of SSNHL.

Loss of central mineralocorticoid or glucocorticoid receptors impacts auditory nerve processing in the cochlea

The key auditory signature that may associate peripheral hearing with central auditory cognitive defects remains elusive. Suggesting the involvement of stress receptors, we here deleted the mineralocorticoid and glucocorticoid receptors (MR and GR) using a CaMKIIα-based tamoxifen-inducible Cre^ERT2/loxP approach to generate mice with single or double deletion of central but not cochlear MR and GR. Hearing thresholds of MRGR^{CaMKIIαCreERT2} conditional knockouts (cKO) were unchanged, whereas auditory nerve fiber (ANF) responses were larger and faster and auditory steady state responses were improved. Subsequent analysis of single MR or GR cKO revealed discrete roles for both, central MR and GR on cochlear functions. Limbic MR deletion reduced inner hair cell (IHC) ribbon numbers and ANF responses. In contrast, GR deletion shortened the latency and improved the synchronization to amplitude-modulated tones without affecting IHC ribbon numbers. These findings imply that stress hormone-dependent functions of central MR/GR contribute to “precognitive” sound processing in the cochlea.

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Top-down MR/GR signaling differentially contributes to cochlear sound processing

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Limbic MR stimulates auditory nerve fiber discharge rates

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Central GR deteriorates auditory nerve fiber synchrony

Association Between the Number of Intratympanic Steroid Injections and Hearing Recovery in Sudden Sensorineural Hearing Loss

The frequency of intratympanic (IT) steroid injection varies from once daily to once weekly or less among studies and does not reach a uniform standard. This study investigated the potential association between the number of IT steroid injections and hearing recovery to determine the optimal number in sudden sensorineural hearing loss (SSNHL) patients. A retrospective study involving 233 SSNHL patients receiving IT steroids plus batroxobin within 7 days of onset was performed. Patients were followed up for 3 months. More than 15 dB of HL improvement in the pretreatment pure tone average (PTA) was defined as effective. The effective group had a higher IT injection numbers than the ineffective group (≥ 6 times: 84.6 vs. 61.1, p < 0.001). Regardless of the unadjusted model or adjusted model, patients who received more frequent IT steroid injections seemed more likely to recover hearing (unadjusted model, OR, 95% CI: 1.25, 1.06-1.48; p = 0.007; adjusted model, OR, 95% CI: 1.21, 1.01-1.45; p = 0.044). Six IT injections had the highest rate of hearing recovery (79.1%). In conclusion, IT injection number was an independent factor that was positively associated with hearing recovery, and the optimal number of IT steroid injections was 6. Batroxobin plus higher number of IT steroid injections showed more effective for treating SSNHL.

Neurobiology of Stress-Induced Tinnitus

Emotional stress has accompanied humans since the dawn of time and has played an essential role not only in positive selection and adaptation to an ever-changing environment, but also in the acceleration or even initiation of many illnesses. The three main somatic mechanisms induced by stress are the hypothalamus-pituitary-adrenal axis (HPA axis), the sympathetic-adreno-medullar (SAM) axis, and the immune axis. In this chapter, the stress-induced mechanisms that can affect cochlear physiology are presented and discussed in the context of tinnitus generation and auditory neurobiology. It is concluded that all of the presented mechanisms need to be further investigated. It is advised that clinical practitioners ask patients about stressful events or chronic stress preceding the tinnitus onset and measure the vital signs. Finally, taking into account that tinnitus itself acts as a stressor, the implementation of anti-stress therapies for tinnitus treatment is recommended.

Evaluating the Efficacy of L-N-acetylcysteine and Dexamethasone in Combination to Provide Otoprotection for Electrode Insertion Trauma

BACKGROUND

Electrode insertion trauma (EIT) during cochlear implantation (CI) can cause loss of residual hearing. L-N-acetylcysteine (L-NAC) and dexamethasone (Dex) have been individually shown to provide otoprotection albeit at higher concentrations that may be associated with adverse effects. Objective/Aims: The aim of this study is to determine whether L-NAC and Dex could be combined to decrease their effective dosage.

MATERIALS AND METHODS

The organ of Corti (OC) explants were divided into various groups: 1) control; 2) EIT; 3) EIT treated with different concentrations of Dex; 4) EIT treated with different concentrations of L-NAC; 5) EIT treated with L-NAC and Dex in combination. Hair cell (HC) density, levels of oxidative stress, proinflammatory cytokines and nitric oxide (NO) was determined.

RESULTS

There was a significant loss of HCs in explants subjected to EIT compared to the control group. L-NAC and Dex in combination was able to provide significant otoprotection at lower concentrations compared to individual drugs.

CONCLUSIONS AND SIGNIFICANCE

A combination containing L-NAC and Dex is effective in protecting sensory cells at lower protective doses than each compound separately. These compounds can be combined allowing a decrease of potential side effects of each compound and providing significant otoprotection for EIT.

The impact of phlebotomy and hydroxyurea on survival and risk of thrombosis among older patients with polycythemia vera

Current guidelines recommend therapeutic phlebotomy for all polycythemia vera (PV) patients and additional cytoreductive therapy (eg, hydroxyurea [HU]) for high-risk PV patients. Little is known about the impact of these therapies in the real-world setting. We conducted a retrospective cohort study of older adults diagnosed with PV from 2007 to 2013 using the linked Surveillance, Epidemiology, and End Results-Medicare database. Multivariable Cox proportional hazards models were used to assess the effect of phlebotomy and HU on overall survival (OS) and the occurrence of thrombotic events. Of 820 PV patients (median age = 77 years), 16.3% received neither phlebotomy nor HU, 23.0% were managed with phlebotomy only, 19.6% with HU only, and 41.1% with both treatments. After a median follow-up of 2.83 years, 37.2% (n = 305) of the patients died. Phlebotomy (yes/no; hazard ratio [HR] = 0.65; 95% confidence interval [CI], 0.51-0.81; P < .01), increasing phlebotomy intensity (HR = 0.71; 95% CI, 0.65-0.79; P < .01), and a higher proportion of days covered (PDC) by HU were all significantly associated with lower mortality. When thrombosis was the outcome of interest, phlebotomy (yes/no; HR = 0.52; 95% CI, 0.42-0.66; P < .01) and increasing phlebotomy intensity (HR = 0.46; 95% CI, 0.29-0.74; P < .01) were significantly associated with a lower risk of thrombotic events, so was a higher HU PDC. In this population-based study of older adults with PV reflecting contemporary clinical practice, phlebotomy and HU were associated with improved OS and decreased risk of thrombosis. However, both treatment modalities were underused in this cohort of older PV patients.

Effects of stress on the auditory system: an approach to study a common origin for mood disorders and dementia

The concept of stress is a fundamental piece to understand how organisms can adapt to the demands produced by a continuously changing environment. However, modern lifestyle subjects humans to high levels of negative stress or distress, which increases the prevalence of mental illnesses. Definitely, stress has become the pandemic of the 21st century, a fact that demands a great intellectual effort from scientists to understand the neurobiology of stress. This review proposes an innovative point of view to understand that mood disorders and dementia have a common etiology in a stressful environment. We propose that distress produces sensory deprivation, and this interferes with the connection between the brain and the environment in which the subject lives. The auditory system can serve as an example to understand this idea. In this sense, distress impairs the auditory system and induces hearing loss or presbycusis at an early age; this can increase the cognitive load in stressed people, which can stimulate the development of dementia in them. On the other hand, distress impairs the auditory system and increases the excitability of the amygdala, a limbic structure involved in the emotional processing of sounds. A consequence of these alterations could be the increase in the persistence of auditory fear memory, which could increase the development of mood disorders. Finally, it is important to emphasize that stress is an evolutionary issue that is necessary to understand the mental health of humans in these modern times. This article is a contribution to this discussion and will provide insights into the origin of stress-related neuropsychiatric disorders.

Advances and Challenges in Pharmaceutical Therapies to Prevent and Repair Cochlear Injuries From Noise

Noise induces a broad spectrum of pathological injuries to the cochlea, reflecting both mechanical damage to the delicate architecture of the structures of the organ of Corti and metabolic damage within the organ of Corti and lateral wall tissues. Unlike ototoxic medications, the blood-labyrinth barrier does not offer protection against noise injury. The blood-labyrinth barrier is a target of noise injury, and can be weakened as part of the metabolic pathologies in the cochlea. However, it also offers a potential for therapeutic intervention with oto-protective compounds. Because the blood-labyrinth barrier is weakened by noise, penetration of blood-borne oto-protective compounds could be higher. However, systemic dosing for cochlear protection from noise offers other significant challenges. An alternative option to systemic dosing is local administration to the cochlea through the round window membrane using a variety of drug delivery techniques. The review will discuss noise-induced cochlear pathology, including alterations to the blood-labyrinth barrier, and then transition into discussing approaches for delivery of oto-protective compounds to reduce cochlear injury from noise.

Circadian integration of inflammation and glucocorticoid actions: Implications for the cochlea

Auditory function has been shown to be influenced by the circadian system. Increasing evidence point towards the regulation of inflammation and glucocorticoid actions by circadian rhythms in the cochlea. Yet, how these three systems (circadian, immune and endocrine) converge to control auditory function remains to be established. Here we review the knowledge on immune and glucocorticoid actions, and how they interact with the circadian and the auditory system, with a particular emphasis on cochlear responses to noise trauma. We propose a multimodal approach to understand the mechanisms of noise-induced hearing loss by integrating the circadian, immune and endocrine systems into the bearings of the cochlea. Considering the well-established positive impact of chronotherapeutic approaches in the treatment of cardiovascular, asthma and cancer, an increased knowledge on the mechanisms where circadian, immune and glucocorticoids meet in the cochlea may improve current treatments against hearing disorders.

Impact of Hydroxyurea on Survival and Risk of Thrombosis Among Older Patients With Essential Thrombocythemia

Background: Current guidelines recommend hydroxyurea (HU) as frontline therapy for patients with high-risk essential thrombocythemia (ET) to prevent thrombosis. However, little is known about the impact of HU on thrombosis or survival among these patients in the real-world setting. Patients and Methods: A retrospective cohort study was conducted of older adults (aged ≥66 years) diagnosed with ET from 2007 through 2013 using the linked SEER-Medicare database. Multivariable Cox proportional hazards regression models were used to assess the effect of HU on overall survival, and multivariable competing risk models were used to assess the effect of HU on the occurrence of thrombotic events. Results: Of 1,010 patients, 745 (73.8%) received HU. Treatment with HU was associated with a significantly lower risk of death (hazard ratio [HR], 0.52; 95% CI, 0.43–0.64; P<.01). Every 10% increase in HU proportion of days covered was associated with a 12% decreased risk of death (HR, 0.88; 95% CI, 0.86–0.91; P<.01). Compared with nonusers, HU users also had a significantly lower risk of thrombotic events (HR, 0.51; 95% CI, 0.41–0.64; P<.01). Conclusions: Although underused in our study population, HU was associated with a reduced incidence of thrombotic events and improved overall survival in older patients with ET.

Exploring regulatory networks of miR-96 in the developing inner ear

Mutations in the microRNA Mir96 cause deafness in mice and humans. In the diminuendo mouse, which carries a single base pair change in the seed region of miR-96, the sensory hair cells crucial for hearing fail to develop fully and retain immature characteristics, suggesting that miR-96 is important for coordinating hair cell maturation. Our previous transcriptional analyses show that many genes are misregulated in the diminuendo inner ear and we report here further misregulated genes. We have chosen three complementary approaches to explore potential networks controlled by miR-96 using these transcriptional data. Firstly, we used regulatory interactions manually curated from the literature to construct a regulatory network incorporating our transcriptional data. Secondly, we built a protein-protein interaction network using the InnateDB database. Thirdly, gene set enrichment analysis was used to identify gene sets in which the misregulated genes are enriched. We have identified several candidates for mediating some of the expression changes caused by the diminuendo mutation, including Fos, Myc, Trp53 and Nr3c1, and confirmed our prediction that Fos is downregulated in diminuendo homozygotes. Understanding the pathways regulated by miR-96 could lead to potential therapeutic targets for treating hearing loss due to perturbation of any component of the network.

Preoperative steroids for hearing preservation cochlear implantation: A review

Preoperative steroids have been shown to be beneficial in reducing the hearing loss associated with cochlear implantation. This review article discusses the mechanism of action, effects of differing routes of administration, and side effects of steroids administered to the inner ear. Studies on the role of preoperative steroids in animal and human studies are also examined and future directions for research in this area are discussed.

Dexamethasone loaded nanoparticles exert protective effects against Cisplatin-induced hearing loss by systemic administration

Ototoxicity is one of the most important adverse effects of cisplatin chemotherapy. As a common treatment of acute sensorineural hearing loss, systemic administration of steroids was demonstrated ineffective against cisplatin-induced hearing loss (CIHL) in published studies. The current study aimed to evaluate the potential protective effect of dexamethasone (DEX) encapsulated in polyethyleneglycol-coated polylactic acid (PEG-PLA) nanoparticles (DEX-NPs) against cisplatin-induced hearing loss following systemic administration. DEX was fabricated into PEG-PLA nanoparticles using emulsion and evaporation technique as previously reported. DEX or DEX-NPs was administered intraperitoneally to guinea pigs 1h before cisplatin administration. Auditory brainstem response (ABR) threshold shifts were measured at four frequencies (4, 8, 16, and 24kHz) 1 day before and three days after cisplatin injection. Cochlear morphology was examined to evaluate inner ear injury induced by cisplatin exposure. A single dose of DEX-NPs 1h before cisplatin treatment resulted in a significant preservation of the functional and structural properties of the cochlea, which was equivalent to the effect of multidose (3 days) DEX injection. In contrast, no significant protective effect was observed by single dose injection of DEX. The results of histological examination of the cochleae were consistent with the functional measurements. In conclusion, a single dose DEX-NPs significantly attenuated cisplatin ototoxicity in guinea pigs after systemic administration at both histological and functional levels indicating the potential therapeutic benefits of these nanoparticles for enhancing the delivery of DEX in acute sensorineural hearing loss.

Prophylactic and therapeutic functions of drug combinations against noise-induced hearing loss

Noise is the most common occupational and environmental hazard. Noise-induced hearing loss (NIHL) is the second most common form of sensorineural hearing deficit, after age-related hearing loss (presbycusis). Although promising approaches have been identified for reducing NIHL, currently there are no effective medications to prevent NIHL. Development of an efficacious treatment has been hampered by the complex array of cellular and molecular pathways involved in NIHL. We turned this difficulty into an advantage by asking whether NIHL could be effectively prevented by targeting multiple signaling pathways with a combination of drugs already approved by U.S. Food and Drug Administration (FDA). We previously found that antiepileptic drugs blocking T-type calcium channels had both prophylactic and therapeutic effects for NIHL. NIHL can also be reduced by an up-regulation of glucocorticoid (GC) signaling pathways. Based on these findings, we tested a combination therapy for NIHL that included ethosuximide and zonisamide (anticonvulsants) and dexamethasone and methylprednisolone (synthetic GCs) in mice under exposure conditions typically associated with dramatic permanent threshold shifts (PTS). We first examined possible prophylactic effects for each drug when administered alone 2 h before noise, and calculated the median effective dose (ED50). We then tested for synergistic effects of two-drug combinations (anticonvulsant + GC), and identified combinations with the strongest synergy against NIHL, based on a previously established combination index (CI) metric. We repeated similar tests to determine their therapeutic effects when administered the same drugs 24 h after the noise exposure. Our study shows the feasibility of developing pharmacological intervention in multiple pathways, and discovering drug combinations with optimal synergistic effects in preventing permanent NIHL.

Expression and dexamethasone-induced nuclear translocation of glucocorticoid and mineralocorticoid receptors in guinea pig cochlear cells

Glucocorticoids (GC) are powerful anti-inflammatory agents frequently used to protect the auditory organ against damage associated with a variety of conditions, including noise exposure and ototoxic drugs as well as bacterial and viral infections. In addition to glucocorticoid receptors (GC-R), natural and synthetic GC are known to bind mineralocorticoid receptors (MC-R) with great affinity. We used light and laser scanning confocal microscopy to investigate the expression of GC-R and MC-R in different cell populations of the guinea pig cochlea, and their translocation to different cell compartments after treatment with the synthetic GC dexamethasone. We found expression of both types of receptors in the cytoplasm and nucleus of sensory inner and outer hair cells as well as pillar, Hensen and Deiters cells in the organ of Corti, inner and outer sulcus cells, spiral ganglion neurons and several types of spiral ligament and spiral limbus cells; stria vascularis cells expressed mostly MC-R whereas fibrocytes type IV were positive for GC-R only. GC-R and MC-R were also localized at or near the plasma membrane of pillar cells and outer hair cells, whereas GC-R were found at or near the plasma membrane of Hensen cells only. We investigated the relative levels of receptor expression in the cytoplasm and the nucleus of Hensen cells treated with dexamethasone, and found they varied in a way suggestive of dose-induced translocation. These results suggest that the oto-protective effects of GC could be associated with the concerted activation of genomic and non-genomic, GC-R and MC-R mediated signaling pathways in different regions of the cochlea.

Corticosterone treatment impairs auditory fear learning and the dendritic morphology of the rat inferior colliculus

Stress leads to secretion of the adrenal steroid hormone corticosterone (CORT). The aim of this study was to determine the effects of chronic CORT administration on auditory and visual fear conditioning. Male Sprague-Dawley rats received CORT (400 mg/ml) in their drinking water for 10 consecutive days; this treatment induces stress levels of serum CORT. CORT impaired fear conditioning (F((1,28)) = 11.52, p < 0.01) and extinction (F((1,28)) = 4.86, p < 0.05) of auditory fear learning, but did not affect visual fear conditioning. In addition, we analyzed the CORT effects on the neuronal morphology of the inferior colliculus (flat neurons, auditory mesencephalon, a key brain area for auditory processing) and superior colliculus (wide-field neurons, related to visual processing) by Golgi stain. CORT decreased dendritic arborization of inferior colliculus neurons by approximately 50%, but did not affect superior colliculus neurons. Thus, CORT had more deleterious effects on the auditory fear processing than the visual system in the brain.

Stress and tinnitus-from bedside to bench and back

The aim of this review is to focus the attention of clinicians and basic researchers on the association between psycho-social stress and tinnitus. Although tinnitus is an auditory symptom, its onset and progression often associates with emotional strain. Recent epidemiological studies have provided evidence for a direct relationship between the emotional status of subjects and tinnitus. In addition, studies of function, morphology, and gene and protein expression in the auditory system of animals exposed to stress support the notion that the emotional status can influence the auditory system. The data provided by clinical and basic research with use of animal stress models offers valuable clues for an improvement in diagnosis and more effective treatment of tinnitus.

Repeated antenatal corticosteroid treatments adversely affect neural transmission time and auditory thresholds in laboratory rats

Antenatal corticosteroid (AC) treatment is given to pregnant women at risk for preterm birth to reduce infant morbidity and mortality by enhancing lung and brain maturation. However, there is no accepted regimen on how frequently AC treatments should be given and some studies found that repeated AC treatments can cause growth retardation and brain damage. Our goal was to assess the dose-dependent effects of repeated AC treatment and estimate the critical number of AC courses to cause harmful effects on the auditory brainstem response (ABR), a sensitive measure of brain development, neural transmission and hearing loss. We hypothesized that repeated AC treatment would have harmful effects on the offspring's ABRs and growth only if more than 3 AC treatment courses were given. To test this hypothesis, pregnant Wistar rats were given either a high regimen of AC (HAC), a moderate regimen (MAC), a low regimen (LAC), or saline (SAL). An untreated control (CON) group was also used. Simulating the clinical condition, the HAC dams received 0.2mg/kg Betamethasone (IM) twice daily for 6 days during gestation days (GD) 17-22. The MAC dams received 3 days of AC treatment followed by 3 days of saline treatment on GD 17-19 and GD 20-22, respectively. The LAC dams received 1 day of AC treatment followed by 5 days of saline treatment on GD 17 and GD 18-22, respectively. The SAL dams received 6 days of saline treatment from GD 17 to 22 (twice daily, isovolumetric to the HAC injections, IM). The offspring were ABR-tested on postnatal day 24. Results indicated that the ABR's P4 latencies (neural transmission time) were significantly prolonged (worse) in the HAC pups and that ABR's thresholds were significantly elevated (worse) in the HAC and MAC pups when compared to the CON pups. The HAC and MAC pups were also growth retarded and had higher postnatal mortality than the CON pups. The SAL and LAC pups showed little or no adverse effects. In conclusion, repeated AC treatment had harmful effects on the rat offspring's ABRs, postnatal growth and survival. The prolonged ABR latencies reflect slowed neural transmission times along the auditory nerve and brainstem auditory pathway. The elevated ABR thresholds reflect hearing deficits. We concluded that repeated AC treatment can have harmful neurological, sensory and developmental effects on the rat offspring. These effects should be considered when weighing the benefits and risks of repeated AC treatment and when monitoring and managing the prenatally exposed child for possible adverse effects.

Protecting the auditory system with glucocorticoids

Glucocorticoids are hormones released following stress-related events and function to maintain homeostasis. Glucocorticoid receptors localize, among others, to hair cells, spiral ligament and spiral ganglion neurons. Glucocorticoid receptor-induced protection against acoustic trauma is found by i) pretreatment with glucocorticoid agonists; ii) acute restraint stress; and iii) sound conditioning. In contrast, glucocorticoid receptor antagonists exacerbate hearing loss. These findings have important clinical significance since synthetic glucocorticoids are commonly used to treat hearing loss. However, this treatment has limited success since hearing improvement is often not maintained once the treatment has ended, a fact that reduces the overall appeal for this treatment. It must be realized that despite the widespread use of glucocorticoids to treat hearing disorders, the molecular mechanisms underlying this treatment are not well characterized. This review will give insight into some physiological and biochemical mechanisms underlying glucocorticoid treatment for preventing hearing loss.

Stealth-nanoparticle strategy for enhancing the efficacy of steroids in mice with noise-induced hearing loss

AIMS

This study aimed to investigate the efficacy of encapsulating steroids, which is a primary choice for the treatment of sensorineural hearing loss, in polyethylene glycol-coated polylactic acid nanoparticles for drug delivery to the cochlea.

MATERIALS & METHODS

We prepared polyethylene glycol-coated polylactic acid nanoparticles encapsulating rhodamine or betamethasone phosphate (BP), and administered them systemically to CBA/N mice previously exposed to intense noise. We assessed nanoparticle distribution using rhodamine fluorescence, BP concentrations in tissues, nuclear translocation of glucocorticoid receptors and the function and histology of the mouse cochleae.

RESULTS & CONCLUSION

Polyethylene glycol-coated polylactic acid nanoparticles delivered BP to cochleae over a sustained period, resulting in significant reductions in histological and functional damage to cochleae and indicating the potential therapeutic benefits of these nanoparticles for enhancing the delivery of BP in acute sensorineural hearing loss.

The role of glucocorticoids for spiral ganglion neuron survival

Glucocorticoids, which are steroidal stress hormones, have a broad array of biological functions. Synthetic glucocorticoids are frequently used therapeutically for many pathologic conditions, including diseases of the inner ear; however, their exact functions in the cochlea are not completely understood. Recent work has clearly demonstrated the presence of glucocorticoid signaling pathways in the cochlea and elucidated their protective roles against noise-induced hearing loss. Furthermore, indirect evidence suggests the involvement of glucocorticoids in age-related loss of spiral ganglion neurons and extensive studies in the central nervous system demonstrate profound effects of glucocorticoids on neuronal functions. With the advancement of recent pharmacologic and genetic tools, the role of these pathways in the survival of spiral ganglion neurons after noise exposure and during aging should be revealed.

Dexamethasone and methylprednisolone do not inhibit neuritic outgrowth while inhibiting outgrowth of fibroblasts from spiral ganglion explants

CONCLUSION

Dexamethasone and methylprednisolone do not inhibit neuritic outgrowth while inhibiting fibroblastic outgrowth from spiral ganglion micro-explants.

OBJECTIVES

To demonstrate reduced fibroblastic outgrowth while maintaining neurite outgrowth for several corticosteroids using an in vitro test system of neonatal rat spiral ganglion micro-explants.

MATERIALS AND METHODS

The in vitro test system comprised 3-day-old rat spiral ganglion micro-explants. Dexamethasone, methylprednisolone, triamcinolone acetonide, and human recombinant brain-derived neurotrophic factor (hrBDNF) were tested in vitro. The control was ganglion micro-explants in supplemented Dulbecco's modified Eagle's medium. Areas of the ganglion explant, neurite and fibroblast outgrowth of ganglion explants after 10 days in vitro were imaged, digitized, and analyzed using Image Tool 3.00 on a PC workstation. Areas of neurite and fibroblast outgrowth from the experimental explants were compared against values obtained from control explants.

RESULTS

Dexamethasone gave the best result of the three corticosteroids tested for inhibiting fibroblast outgrowth while not inhibiting neurite outgrowth from the ganglion micro-explants. Media containing hrBDNF (10 ng/ml) stimulated significantly greater neurite outgrowth than outgrowth from control explants (p < 0.001). Ganglion micro-explants treated with dexamethasone (0.02 mg/ml) and methylprednisolone (0.5 mg/ml) provided the greatest inhibition of fibroblast outgrowth compared with control explants (p < 0.001).

Mechanisms of noise-induced hearing loss indicate multiple methods of prevention

Recent research has shown the essential role of reduced blood flow and free radical formation in the cochlea in noise-induced hearing loss (NIHL). The amount, distribution, and time course of free radical formation have been defined, including a clinically significant late formation 7-10 days following noise exposure, and one mechanism underlying noise-induced reduction in cochlear blood flow has finally been identified. These new insights have led to the formulation of new hypotheses regarding the molecular mechanisms of NIHL; and, from these, we have identified interventions that prevent NIHL, even with treatment onset delayed up to 3 days post-noise. It is essential to now assess the additive effects of agents intervening at different points in the cell death pathway to optimize treatment efficacy. Finding safe and effective interventions that attenuate NIHL will provide a compelling scientific rationale to justify human trials to eliminate this single major cause of acquired hearing loss.

Glucocorticoid receptor and nuclear factor-kappa B interactions in restraint stress-mediated protection against acoustic trauma

The role of glucocorticoid receptors (GRs) in the protective effect of restraint stress (RS) before acoustic trauma was studied in spiral ganglion neurons of CBA mice. RS increased corticosterone and protected against elevated auditory brain stem thresholds caused by acoustic trauma. This protection was inhibited by the pretreatment with a corticosterone synthesis inhibitor, metyrapone (MET), and a GR antagonist (RU486). RS followed by acoustic trauma caused an immediate increase in corticosterone that triggered nuclear translocation of GR, without a change in the expression of GR protein. RU486 + MET before RS and acoustic trauma caused an immediate increase in GR mRNA followed by increased GR protein expression (24 h after trauma). GR signaling was further characterized by analyzing nuclear factor-kappaB (NF kappaB) nuclear translocation and protein expression. NF kappaB nuclear translocation was reduced after acoustic trauma or pretreatment with RU486 + MET before RS and acoustic trauma. On the contrary, RS protected against the trauma-induced NF kappaB reduction of its nuclear translocation in inhibitory-kappaB (I kappaB)-dependent manner. RU486 + MET caused a simultaneous decreased I kappaB expression and NF kappaB nuclear translocation, demonstrating an interference with the I kappaB-mediated activation of NF kappaB. In summary, RS protects the cochlea from acoustic trauma by increasing corticosterone and activating GRs. These results emphasis how GR activity modulates hearing sensitivity and its importance for the rationale use of glucocorticoids in inner ear diseases.

Triamcinolone acetonide protects auditory hair cells from 4-hydroxy-2,3-nonenal (HNE) ototoxicity in vitro

CONCLUSION

Triamcinolone acetonide crystalline suspension (e.g. Volon A) was not ototoxic to the auditory hair cells present within organ of Corti explants and protected them from an ototoxic molecule, i.e. 4-hydroxy-2,3-nonenal (HNE), that is produced within the organ of Corti as a result of oxidative stress-induced damage.

OBJECTIVES

To test the corticosteroid, triamcinolone acetonide, for ototoxicity and otoprotective capacity in organ of Corti explants.

MATERIALS AND METHODS

Organ of Corti explants excised from 4-day-old rats were the test system, HNE was the ototoxin challenge. Hair cell integrity counts were performed with fluorescent microscopy on fixed explants stained with FITC-labeled phalloidin. Statistical significance was set at p<0.05.

RESULTS

Triamcinolone acetonide did not affect hair cell integrity in the organ of Corti explants and it provided a high level of protection of hair cells against the ototoxic effects of a damaging level of HNE as determined by hair cell density counts.

Pharmakotherapie des akuten Tinnitus

Hypoxia/ischemia may play an important role in the pathogenesis of sensorineural tinnitus due to the characteristics of the cochlear blood supply. In addition, hypoxia modulates molecular processes both in the acute and chronic forms of tinnitus. Transcription factor HIF-1 (hypoxia-inducible factor) may play a key role in the cells' adaptation to hypoxia and ischemia, while under hypoxic/ischemic conditions, HIF-1 induces changes in the gene expression which may contribute to the remodeling of particular structures within the cochlea. Disturbances in the cochlear blood supply may result in membrane changes, perineural edema, inflammation, disturbances in ion homeostasis and in the formation of reactive oxygen species. Thus, the pharmacotherapy of acute tinnitus may be aimed at the improvement of cochlear blood supply and the prevention of acute processes leading to cell damage. Pharmacotherapies with colloidal plasma substitutes, vasodilators, calcium antagonists, procaine, and cortisone have been described in the literature and are discussed here. Many of the pharmacological treatments have not been validated in double blind studies. Although it is impossible to deduce the cause of tinnitus from a drug's efficiency, there is some evidence that it can be effectively suppressed by improving blood supply, at least at certain stages. The aim is to achieve an improved pharmacotherapy by means of sophisticated diagnostic instruments for classifying particular types of tinnitus.

The emotional ear in stress

Stress of some kind is encountered everyday and release of stress hormones is essential for adaptation to change. Stress can be physical (pain, noise exposure, etc.), psychological (apprehension to impending events, acoustic conditioning, etc.) or due to homeostatic disturbance (hunger, blood pressure, inner ear pressure, etc.). Persistent elevated levels of stress hormones can lead to disease states. The aim of the present review is to bring together data describing morphological or functional evidence for hormones of stress within the inner ear. The present review describes possible multiple interactions between the sympathetic and the complex feed-back neuroendocrine systems which interact with the immune system and so could contribute to various inner ear dysfunctions such as tinnitus, vertigo, hearing losses. Since there is a rapidly expanding list of genes specifically expressed within the inner ear this clearly allows for possible genomic and non-genomic local action of steroid hormones. Since stress can be encountered at any time throughout the life-time, the effects might be manifested starting from in-utero. These are avenues of research which remain relatively unexplored which merit further consideration. Progress in this domain could lead towards integration of stress concept into the overall clinical management of various inner ear pathologies.

Localization of glucocorticoid receptors in the murine inner ear

We performed an immunohistochemical investigation of the distribution of glucocorticoid receptors (GRs) in the murine inner ear and found that GRs were expressed extensively, but with various degrees of immunoreactivity in different regions. We observed the strongest GR expression in the type III fibrocytes of the spiral ligament. Although the immunoreactivity of the cochlear hair cells and of the vestibular sensory epithelia was weak, the neighboring cochlear supporting cells and the subepithelial regions of the vestibular sensory epithelia were immunostained. Staining for GRs was also positive in the spiral ganglia and vestibular ganglia, as well as in the endolymphatic sac. The role of GRs in the inner ear is discussed.

Intra-cochlear administration of dexamethasone attenuates aminoglycoside ototoxicity in the guinea pig

This study demonstrates the attenuation of aminoglycoside ototoxicity by cochlear infusion of dexamethasone (Dex) using a microcannulation-osmotic pump delivery system. The results indicate that treating the cochlea with Dex both before and after kanamycin administration was more effective in preventing ototoxicity than Dex treatment only after kanamycin administration. A concentration of 1 ng/ml Dex showed the greatest protective effect on both kanamycin-induced threshold shift of the auditory brainstem response and outer hair cell survival. These results show that the Dex treatment attenuates both functional and structural damage of the inner ear from aminoglycoside toxicity.

The endocrine system, vertigo and balance

Steroid, amine and peptide hormones affect the peripheral vestibular system. Vasopressin hypersensitivity of the endolymphatic sac may be implicated in the pathogenesis of Meniere's disease. Specific vasopressin antagonists will help define the role of vasopressin in Meniere's disease. The modulation of central vestibular pathways by neuroactive steroids may involve effects on gamma-aminobutyric acid-ergic and glutaminergic pathways. The vestibular nuclei also express enzymes that are important in the synthesis of steroids and the modulation of their activity. Steroids mediate both facilitatory and deleterious effects of stress on vestibular compensation. The quality and quantity of stressor that determines the pattern of hormonal output, may be important. Clinical observation suggests that episodic ataxia type 2, a P/Q calcium channelopathy, may be phenotypically modulated by endocrine fluctuations. Steroid hormones may affect the episodic ataxia type 2 phenotype by modulation of voltage-gated calcium channel activity via second messenger systems and ion channel subunit expression. Despite evidence to support the link, the role of the endocrine system in vestibular function and disease is as yet virtually unexplored.

A role of glucocorticoid receptors in the guinea pig vestibular system

To investigate glucocorticoid receptor (GR) function in the vestibular periphery, GR antagonist RU38486 was administered to the guinea pig inner ear by osmotic pump, and we observed post-rotatory nystagmus (PRN) changes as a marker of vestibular function. Ten days after treatment, RU38486 (1 mM) resulted in ipsilateral vestibule hyperexcitability in response to rotation stimulation. This effect was dose-dependent. These data indicate that steroid hormones may play an important role in maintaining vestibular function.

Developmental expression patterns of connexin26 and -30 in the rat cochlea

Connexin proteins form transmembranous gap junction channels that connect adjacent cells. Connexin26 and connexin30 have been previously shown to be strongly expressed in the inner ear of adult rats and to be mainly colocalized. Because intercellular connections by gap junction proteins are crucial for maturation of different tissues, we investigated the developmental expression of connexin26 and connexin30 in pre- and postnatal rats using immunocytochemistry. In the rat otocyst, staining for connexin26 as well as for connexin30 appeared at the 17th day of gestation. However, at this stage, expression of connexin30 was low and restricted to the neurosensory epithelium. Beginning from the 3rd postnatal day connexin26 and -30 were expressed with highest immunoreaction in the spiral limbus, the neurosensory epithelium, and between the stria vascularis and the spiral ligament. Beginning from postnatal day 12 the staining pattern resembled that of adult animals, with additional strong staining between all fibrocytes of the spiral ligament. Double labeling experiments demonstrated strongest colocalization of both connexins between the stria vascularis and the spiral ligament. These results demonstrate that development of the cochlear gap junction system precedes the functional maturation of the rat inner ear, which takes place between the 2nd and 3rd postnatal week. In the cochlea of a 22-week-old human embryo, connexin26 and connexin30 could be detected in the lateral wall, suggesting that both connexins also play a crucial role in function of the human inner ear.

Steroid treatment improves cochlear function in the MRL.MpJ-Fas(lpr) autoimmune mouse

Corticosteroid therapy is used to reverse autoimmune sensorineural hearing loss, although little is known of the mechanism by which this occurs. This has been due to the lack of a suitable animal model with spontaneous hearing loss that is steroid responsive. The present study examined the effects of prednisolone treatment on auditory thresholds in the MRL.MpJ-Fas(lpr) autoimmune mouse to determine its suitability as such a model. Autoimmune mice at 3.5-4. 5 months of age were evaluated by pure-tone auditory brainstem response (ABR) to establish threshold elevations due to the disease. The steroid treatment group was then given prednisolone in their drinking water for 2.5 months, while untreated controls were given tap water. Significantly more steroid treated mice survived to the time of post-treatment ABR evaluation. Half of the steroid treated ears demonstrated either improvement or no change in cochlear function compared to only 25% in the untreated controls. Overall, cochlear thresholds in the untreated controls increased by 14.7 dB, whereas no significant threshold increase was seen in the steroid treated group (4.3 dB) over the treatment period. No qualitative anatomical differences were seen in the ears of those mice surviving to the end of the study. These findings establish the autoimmune mouse as a model for studies of steroid responsive mechanisms within the ear. This could apply to autoimmune sensorineural hearing loss, as well as any hearing disorder for which steroid therapy is recommended.

Distribution of Na,K-ATPase is normal in the inner ear of a mouse with a null mutation of the glucocorticoid receptor

This study was performed in order to test the hypothesis that the glucocorticoid hormone stimulates the formation of Na,K-ATPase in the inner ear of the mouse. An immunohistochemical study with respect to the presence and distribution of glucocorticoid receptors (GR) and Na,K-ATPase in the vestibular and cochlear regions of the inner ear was performed on a C57BL mouse with a null mutation of the glucocorticoid receptor (GR mutant mouse). The wild type C57BL mouse and the CBA mouse served as normal controls. As expected, the homozygous GR mutant mouse showed no specific staining for GR in the inner ear. The heterozygous GR mutant mouse showed faint staining of GR in the spiral limbus, the spiral ganglion, the organ of Corti and the utricle. This staining was markedly less than in the wild type C57BL mouse. Antibody labelling of Na,K-ATPase in the inner ear showed no significant difference between the homozygous and the heterozygous GR mutant mouse as compared to the control wild type C57BL mouse or the CBA mouse. Although earlier studies have shown a positive correlation between levels of glucocorticoid hormone in serum and the concentration of Na,K-ATPase in the inner ear, the hypothesis that glucocorticoid hormones alone stimulate the formation of Na,K-ATPase in the inner ear could not be confirmed by this study. Thus other regulating substances must be considered.

The effect of prednisolone and non-steroidal anti-inflammatory agents on the normal and noise-damaged guinea pig inner ear

The effect of anti-inflammatory agents, such as the synthetic glucocorticoid prednisolone, diclofenac sodium, and histamine H1-receptor antagonist, was studied in unexposed and noise-exposed (broad-band noise, bandwidth 1-12 kHz, 106 dB SPL, 30 min) guinea pigs. The results were compared with the results obtained from no treatment and with isotonic saline (placebo) therapy. The cochlear blood flow (CoBF) and the partial oxygen pressure in the perilymph (PL-pO2) were continuously and simultaneously recorded over a period of 210 min. In addition, cochlear microphonics (CMs), compound action potentials of the auditory nerve (CAPs), and auditory brain stem responses (ABRs) were registered. Noise-induced hearing loss paralleled a decrease of PL-pO2. Both were found to occur before evidence of reduced CoBF. PL-pO2 and CoBF progressively declined post-exposure, while CMs, CAPs, and ABRs did not further deteriorate nor showed signs of recovery up to 180 min after cessation of noise. Treatment started 60 min post-exposure, or after 90 min without manipulation and was then further studied for 120 min. In the unexposed animals, diclofenac sodium and prednisolone induced a significant decline of PL-pO2, while CoBF, CMs, CAPs, and ABRs revealed no change. Isotonic saline did not influence the measured parameters. After infusion of the histamine H1-receptor antagonist, a significant decrease of CoBF together with blood pressure and CMs was observed, while PL-pO2, CAPs, and ABRs showed no change. In the noise-exposed animals, diclofenac sodium induced partial restoration of CM and CAP amplitudes and full restoration of ABRs. Following a high dose of prednisolone (25 mg), partial restoration of CMs and full restoration of CAPs and ABRs were registered. This effect was significantly less pronounced following a low dose of prednisolone (2.5 mg). Restoration of CMs, CAPs, and ABRs was immediate (i.e. 50 min after infusion) and remained stable for another 60 min until the end of the recording period. The histamine H1-receptor antagonist and isotonic saline did not influence CMs, CAPs, and ABRs. None of the applied drugs resulted in relief of progressive noise-induced cochlear hypoxia and post-traumatic ischemia. These findings indicate direct cellular effects of prednisolone and diclofenac sodium in the cochlea taking into account no blood flow and oxygenation. The possible mechanisms involved are discussed.

Development of 11 beta-hydroxysteroid dehydrogenase expression in the rat cochlea

11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) catalyzes the transformation of active glucocorticoid (GC) steroids to inactive 11-oxosteroids, as well as the reverse reaction. 11 beta-HSD was previously demonstrated specifically in the spiral ligament of the lateral cochlear wall where it was co-localized with adrenal steroid receptors. These findings imply that 11 beta-HSD regulates binding of corticoids to their inner ear receptors. The GC receptor expression initially occurs around the critical maturation period of the cochlear duct. 11 beta-HSD, which is an integral part of the cochlear steroid receptor system, could indirectly affect glucocorticoid-mediated induction processes. In this study the expression of 11 beta-HSD was studied in the postnatal rat cochlea from the 3rd to 30th postnatal day. Bouin's fixed, paraffin-embedded cochlear sections were processed for immunocytochemical detection of 11 beta-HSD using polyclonal antibodies against 11 beta-HSD. 11 beta-HSD expression appeared at the 12th postnatal day at low levels in spiral ligament tissues. From the 15th postnatal day, 11 beta-HSD expression was stronger and similar to that of the adult cochlea. No additional inner ear tissue region expressed 11 beta-HSD enzyme during the observed period. 11 beta-HSD expression coincides with the onset of functional maturity of the rat cochlear duct. The expression of 11 beta-HSD is preceded by the expression of GC receptors which appeared at the 7th postnatal day in the rat cochlea. These results further suggest an integrative role of the cochlear steroid receptor system in the homeostasis and functional maturation of the cochlea.

Na,K-ATPase alpha- and beta-isoforms in the developing cochlea of the mouse

Immunohistochemistry was used to investigate the presence of Na,K-ATPase alpha- and beta-subunits isoforms (alpha 1, alpha 2, alpha 3, beta 1 and beta 2) in the cochlea of the mouse at different ages between embryological day (E) 19 and postnatal day (P) + 30. alpha 1 was mainly found in the stria vascularis and in the spiral ligament; it increased steadily from p+4. These data correlates well with the morphological and electrophysiological maturation of the cochlea. alpha 3 predominated in the spiral ganglia and the cochlear nerve. This finding is well in accordance with reports that alpha 3 seems to be associated with the nervous system. The beta-subunit was found mainly in those tissues where staining of the alpha-subunit also was seen. Both subunits were localized in tissue regions where fluid regulation is expected to play an important role. For some isoforms, the expression pattern of Na,K-ATPase during development in the mouse is different from that in the rat. The expression of Na,K-ATPase and that of glucocorticoid receptors during development in the inner ear of the mouse show a similar pattern, which may indicate that glucocorticoid receptors could be involved in regulating the expression of Na,K-ATPase.

Appearance of glucocorticoid receptors in the inner ear of the mouse during development

CBA mice were sacrificed at different ages of developments at embryonic day 13 (E13), E14, E16, E19, E20 and postnatal day 1 (P1), P2, P3, P4, P6, P8, P10, P14, P16, P18, P20 and P30. The temporal bones were quickly removed and deep frozen in order to prepare cryosections for immunohistochemical staining with polyclonal antibodies against glucocorticoid receptors. The avidin-biotin, ABC-method was used to visualize binding. Both the vestibular and the cochlear regions of the inner ear were analysed. A faint staining of the crista ampullaris, the utricle and the cochlear duct was seen at E19; and staining became clearly visible at P1. A decrease in labelling was found at day 2-5 post partum whereafter an increased staining was again noticed until postnatal day 14 when an adult pattern was observed. The appearance of glucocorticoid receptors in the inner ear during development does not follow a linear curve. Further, the labelling pattern may indicate an impact of glucocorticoid receptors on the embryologic maturation itself as well as a functional role in the adult ear.

The role of adrenocortical steroid hormones in the development of hearing

Based on the findings that adrenocortical hormones are involved in the regulation of Na+, K(+)-ATPase in several tissues and the presence of receptors for these hormones in the ear during auditory development, it has been suggested that these hormones also induce Na+, K(+)-ATPase activity and the endocochlear potential in the ear, leading to auditory function in the fetus-neonate. In order to test this hypothesis, glucocorticoid and mineralocorticoid hormones were injected into rat pups and their auditory development, compared to control litter-mates, was tested by recording auditory nerve-brainstem evoked potentials (ABR). Those who received glucocorticoid hormones had elevated ABR thresholds on post-natal day (PND) 9, others on PND 11 and still others on PND 16, compared to control litter-mates. The ABR thresholds of those injected with mineralocorticoids were not different from those in controls. These results and additional considerations related to the time sequence of the natural appearance of these hormones in the plasma, of their receptors in the ear and the onset of hearing in rat pups makes it extremely unlikely that adrenocortical hormones are involved in the initiation of Na+, K(+)-ATPase pumps and thereby of the endocochlear potential in the inner ear. It is possible that these hormones and their receptors play a role in the later regulation of the number of pumps.